Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item THE ASSEMBLY STATE OF A BACTERIAL MICROCOMPARTMENT AND ITS RELATED STRUCTURES(2022) Trettel, Daniel; Winkler, Wade; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bacterial microcompartments (BMCs) are polyhedral, protein-based organelles present in a wide range of bacteria. This mode of compartmentalization is highly modular and can accommodate a wide range of chemistries within them, including carbon fixation. These aspects make them a promising target to serve as bioplatforms for commodity chemical synthesis and enhanced carbon fixation. However, it is challenging to investigate the structure and function of BMCs using classical methods. As such, the native structure of BMCs remains largely enigmatic, hampering their synthetic adaption. This dissertation addresses these concerns by describing the assembly state of the model 1,2-propanediol (Pdu) BMC using a variety of approaches. Chemical probing reveals the Pdu BMC is surprisingly permeable to and permissive of derivatization. This insight enabled application of crosslinking mass spectrometry to describe its protein interactome. The interactome map reveals that small domains called encapsulation peptides dominate interior interactions while reporting on the organization of the outer protein shell. Laser scanning confocal approaches were developed to study the solution behavior of BMCs. These experiments heavily suggest that the Pdu BMC is a dynamic entity that exchanges protein elements; a result we primarily attribute to the protein shell. These confocal microscopy approaches were further used to study the super-structures formed by individual shell proteins and to describe their interactions with one another. Together, the results from this project give important insight on the assembly state of the model Pdu BMC including its biogenesis, organization, and behavior. These data answer some of the open questions concerning the assembly of BMC structures, which will help innovate the next generation of BMC-based biotechnology tools.Item Processing-Structure-Microstructure-Property Relationships in Polymer Nanocomposites(2008-01-31) Kota, Arun Kumar; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The optimal development of polymer nanocomposites using carbon nanotube (CNTs) and carbon nanofiber (CNFs) fillers requires a complete understanding of processing-structure-property relationships. The purpose of this understanding is to determine the optimal approach for processing polymer nanocomposites with engineered microstructures and enhanced material properties. In this research, two processing techniques were investigated: solvent processing and twin screw extrusion. The former is a batch process which employs mixing a polymer solution with a filler suspension using long mixing times and low levels of shear mixing. The latter is a continuous process that mixes polymer melts with solid nanoscale ingredients using high levels of shear mixing for a short mixing time. Previous studies conducted on polymer-CNT/CNF using these processes have focused mainly on processing-microstructure and structure-property relationships using one technique or the other. This research focuses on understanding the processing-property relationships by comparing the structure-property relationships resulting from the two processes. Furthermore, the effect of ingredients and processing parameters within each process on microstructure and structure-property relationships was investigated. The microstructural features, namely, distribution of agglomerates, dispersion, alignment, and aspect ratio of the filler were studied using optical, scanning electron, confocal and transmission electron microscopy, respectively. The composition of the filler was determined using thermogravimetric analysis. The electrical, rheological, thermo-oxidative and mechanical properties of the composites were also investigated. Many significant insights related to processing-structure-property relationships were obtained including: (a) deagglomeration is a critical combination of the magnitude of shear rate and the residence time, (b) the structure-property relationships can be modeled using a new methodology based on the degree of percolation by representing the material as an interpenetrating phase composite, (c) annealing can re-establish interconnectivity and improve electrical properties, (d) the degree of dispersion can be resolved using thermogravimetric analysis, and (e) increasing extrusion speed inhibits thermal decomposition and begins to asymptotically increase strength and stiffness through reduction in aspect ratio and size of agglomerates. Finally, a new combinatorial approach was developed for rapidly determining processing-structure relationships of polymer nanocomposites. This dissertation has broad implications in the processing of high performance and multifunctional polymer nanocomposites, combinatorial materials science, and histopathology.